A known rotor system of this kind is used in a BMX freestyle bicycle (bicycle moto cross) for purposes of preventing the brake cables from winding in the case of steering motions and front wheel turns of more than 180.degree.. To this end, the handlebar stem mounts above the frame-mounted steering head tube with the steering head sets for supporting the fork, two annular transmission elements, which are axially held together and capable of rotating relative to each other. A clearance between the handlebar stem and the transmission elements permits the latter to be rotated likewise relative to the handlebar stem. From the brake lever on the handlebar and from the brake on the rear wheel, one brake cable line each extends to one of the transmission elements and is attached thereto. To prevent canting, each brake cable line is present in duplicate and attached in places of the transmission elements that are opposite to one another in the circumferential direction.